CPVC Pipe for ASME SS Exchanger

[mghawar]

Hi,

I am working on a low pressure sugar solution system. A shell&tube exchanger is used to maintain temperature in the system. The sugar solution flows through the tube side (process side, 25psi and 80ºC max)and superheated steam under vacuum is used on the shell side (100 torr and 176ºC max). My question is does this exchanger fall under ASME regulations? Can tube side be ASME vessel and shell non-ASME? Can we use CPVC pipe around the tube side of exchanger that is 304SS? Any help would be greatly appreciated.

Thank very much!

 

[SnTMan]

mghawar, unless it can be exempted by volume, or is not requred by your jursidiction it appears the tubeside would (could) be subject to Sec VIII, Div 1. It appears the shell side could be exempted based on a vacuum-only design pressure, assuming 100 Torr does not exceed 15 psi vacuum (sorry, no handy conversion available).

Either or both sides of a HX can be exempted, depending on the design conditions and this is fairly common. Not sure I'd use CPVC, which I take to mean plastic, at 176 C though.

You probably really should check with your insurance carrier to see what is needed.

Regards,

Mike

 

[mghawar]

Thanks Mike. This helps.

Use of CPVC (which is plastic) would be on the low temperature side maximum 80ºC. The question is that can we have a spec break from exchanger that is 304SS to CPVC pipe. Are there any code regulations that do not allow this (if the exchanger was ASME vessel)?

Thanks,
MG

 

[SnTMan]

mghawar, I am confused on your design conditions, 80 C & 176 C on which sides? Again, you need to check with your insurance carrier to find what is required. Also, double posting (ASME Code Issues forum) is generally frowned upon

Regards,

Mike

 

[mghawar]

Mike,

Thanks for the heads up :s Let's just excuse it once for first time user

Steam on the shell side is at 176C with all SS piping and sugar solution on tube side with maximum 80C temperature with CPVC piping.

Thanks,
mg

 

[SnTMan]

mghawar, is (are) your questions(s) about the heat exchanger or the connected piping?

 

[moltenmetal]

Liquid filled circulating systems where the only source of pressure is a pump, where pressures are modest (below 600 psig) and the fluid is water, or something with a hazard similar to that of water, are often exempted from consideration under pressure vessel and pressure piping code rules. There's generally a "water heater exemption", intended to avoid registering every domestic hot water storage/heating tank as an ASME vessel and the piping as code pressure piping, which these systems fall under. You'd need to check the rules in your own jurisdiction to be sure.

Irrespective of that, CPVC is a piping material permitted for normal fluid service (subject to certain restrictions that don't apply to your sugar solution) under ASME B31.3 pressure piping code, so you could use it even if the system does end up being considered pressure piping. 80 C would be considered a maximum continuous service temperature, so for your application operating at 25 psig and max 80 C it **might** be OK- as long as you have controls to prevent the steam system from overheating the process fluid beyond that 80 C max.

Your steam system sounds really strange- why on earth would you be using superheated steam at 100 torr and 176 C? What matters though is not the operating pressure but the RELIEF PRESSURE of your steam system, which for 176 C sounds suspiciously like 150 psig saturated steam to me. If the relief valve is set higher than 15 psig, you're into the region where your exchanger may need to be ASME designed/constructed (depending on size and design) as a pressure vessel, and your piping on the steam side would be regulated pressure piping- again, depending on the rules in your jurisdiction.

 

[mghawar]

Thanks a lot moltenmetal, this information helps. I have gone through the code and other regional requirements. This is a mechanical recompression system, the evaporated steam from the process is re-compressed through a blower. Steam is superheated due to recompression and is used to recycle heat back into the process.